1. Field of the Invention
The present invention relates to a liquid crystal display (LCD) device, and more particularly, to a transflective LCD device for a mobile communication system, using a dispensing method.
2. Description of the Related Art
In general, a liquid crystal display (LCD) device has a first substrate that includes a thin film transistor (TFT), a second substrate that includes a color filter layer, and a liquid crystal material layer interposed therebetween. Fabrication of a liquid crystal cell of the LCD device includes formation of a common electrode and a pixel electrode on opposing surfaces of the first and second substrates, respectively, and the liquid crystal material is injected through an injection hole between the first and second substrates. A polarizing plate is attached on an outer surface of each of the first and second substrates to complete the liquid crystal cell. Accordingly, image data is displayed by the LCD device by adjusting a voltage that is applied to the common and pixel electrodes to control transmittance of the liquid crystal cell.
The complete process for fabricating the liquid crystal cell includes a limited number of individual steps. In contrast, fabrication processes for forming the TFT on the first substrate and forming the color filter layer on the second substrate may be classified into a significant number of individual fabrication steps. The individual fabrication steps include processes of forming an orientation film, forming a cell gap, injecting liquid crystal material into the cell gap, and forming individual liquid crystal cells. The process for injecting liquid crystal material is performed through one of a dip method or a contact method. In the dip method, the bonded first and second substrates are dipped into a vessel containing the liquid crystal material, and a pressure difference between the bonded first and second substrates and the vessel causes injection of the liquid crystal material into the cell gap through the injection hole. In the contact method, the injection hole contacts a surface of the liquid crystal material in the vessel, and a pressure difference between the bonded first and second substrates and the vessel causes injection of the liquid crystal material into the cell gap through the injection hole. Both the dip method and the contact method are time consuming and may cause contamination of the injection hole, thereby deteriorating display quality of the LCD device.
To solve the above problems, a dispensing method is suggested wherein a sealant is printed along a boundary of an array substrate that includes a plurality of individual liquid crystal cells. Then, the liquid crystal material is dropped within a region defined by the sealant using a dispenser. Accordingly, processing time is reduced and a production yield is dramatically improved.
FIGS. 1A to 1C are plan views showing a fabricating process of a liquid crystal cell using a dispensing method according to the related art, and FIGS. 1D to 1F are cross-sectional views of the fabrication process shown in FIGS. 1A to 1C according to the related art, respectively.
In FIGS. 1A and 1D, a first substrate 2 includes a plurality of unit cells “A” and a second substrate 4 (in FIGS. 1B and 1E) includes an array line (not shown), a pixel electrode (not shown), and a switching device (not shown). A sub-color filter layer (not shown) that corresponds to the pixel electrode and a black matrix (not shown) that corresponds to a space between the pixel electrodes are formed on the first substrate 2.
In FIGS. 1B and 1E, a sealant 6 is printed on the second substrate 4 corresponding to a boundary of the plurality of unit cells “A.” A liquid crystal material 8 (in FIG. 1E) is dropped on an inner region of the sealant 6 using a dispenser, and the first substrate 2 is attached to the second substrate 4 to form a LCD panel 10 (in FIG. 1F).
In FIGS. 1C and 1F, a photo mask 12 (in FIG. 1F) includes a transmissive portion “B” and a blocking portion “C” that are disposed over the LCD panel 10 (in FIG. 1F) for hardening of the sealant 6 by exposure to ultraviolet (UV) light. The transmissive portion “B” corresponds to a position of the sealant 6 of the LCD panel 10, and the blocking portion “C” correspond to an interior position “D” of each of the unit cells “A” (in FIG. 1C). The interior “D” of each of the unit cells “A” provides a mask to prevent a channel region of the TFT on the second substrate 4 from being exposed to the ultraviolet light during the hardening of the sealant 6. Then, the first and second substrates 2 and 4 are fully attached through a subsequent hot press process. Finally, the attached substrates are cut (diced) into individual unit cells “A.”
FIG. 2 is a plan view showing a second substrate of a unit cell according to the related art. In FIG. 2, a second substrate 20 includes a display portion “E” and a surrounding portion “F.” A plurality of array lines (not shown), a plurality of switching devices (not shown), and a plurality of pixel electrodes (not shown) are formed within the display portion “E.” A pad portion “J” is formed to extend from the plurality of array lines at the surrounding portion “F.” The pad portion “J” is formed within a region that will be covered with a case of a mobile communication system.
FIG. 3 is a magnified plan view of partial regions “G”, “H,” and “I” of FIG. 2 according to the related art. In FIG. 3, a second substrate 20 includes a gate line 26 and a data line 28. The gate line 26 includes a gate pad 24 formed within a specific area at one end of the gate line 26. The gate line 26 crosses the data line 28 at a crossing point with an insulating layer (not shown) interposed therebetween, thereby defining a pixel region “P.” The data line 28 includes a data pad 30 formed within a specific area at one end of the data line 28. In general, the gate pads 24 and the data pad 30 are disposed within the surrounding portion “F” of the second substrate 20, and an external signal is applied to the gate pad 24 and the data pad 30. A TFT “T” includes a gate electrode 32, an active layer 34 formed on the gate electrode 32, and a source electrode 36 and a drain electrode 38 formed on both ends of the active layer 34. The TFT “T” is disposed adjacent to the crossing point of the gate line 26 and the data line 28. A transflective electrode 40 is formed on the pixel region “P” and is connected to the drain electrode 38 for applying the external signal that drives a liquid crystal layer (not shown). The transflective electrode 40 defines a reflective portion “K” and a transmissive portion “L,” and includes a reflective electrode 40a having a transmissive hole 42 and a transmissive electrode 40b formed over or under the reflective electrode 40a with an insulating layer (not shown) interposed therebetween. A sealant (not shown) is formed at the surrounding portion “F” (of FIG. 2) of the array substrate 20.
FIG. 4 is a cross-sectional view taken along IV-IV of FIG. 3 according to the related art, and FIG. 5 is a cross-sectional view taken along V-V of FIG. 3 according to the related art. In FIG. 4, an LCD panel “M” for a mobile communication system 50 includes an attached array substrate 20 and a color filter substrate 52, and a liquid crystal material layer 48 disposed therebetween. The LCD panel “M” may be classified into a display portion “E” and a surrounding portion “T.” A backlight 54 is disposed under the LCD panel “M” and is used for a transmissive mode of the LCD panel “M.” A case 56 covers the backlight 54 and the surrounding portion “F” of the LCD panel “M” in FIG. 5.
As shown in FIG. 5, an LCD device fabricated using the dispensing method, a black matrix 58 should not be formed within a region where the sealant 46 is formed. Accordingly, a width of the black matrix 58 at the surrounding portion “E” (in FIG. 4) is about one-half of a width for an LCD device fabricated using the injecting method.
FIG. 6 is a cross-sectional view illustrating a relationship between widths of a black matrix and a sealant according to the related art. In FIG. 6, a width of a surrounding portion is 2.8 mm and a width of a black matrix 58 is reduced to an amount “a” that is about one-half of a width of a black matrix for a LCD device fabricated by the injecting method. The black matrix 58 is spaced apart from a sealant 46 by an amount “β1.” For the sealant having a width of “γ,” since the sealant 46 is formed at a portion spaced apart from an edge of a mobile communication system by an amount “β2,” the surrounding portion of the mobile communication system is designed to have a width of “α+β1+β2+γ.”
However, as shown in FIG. 5, a light leakage phenomenon may occur in a mobile communication system having a structure according to the related art because light 60 of the backlight 54 under the LCD panel “M” (in FIG. 4) is emitted at a vicinity “S1” of the case 56 through a space “N” between the sealant 46 at the surrounding portion “F” of the LCD panel “M” (in FIG. 4) and the black matrix 58. Therefore, a display quality of an LCD device according to the related art is deteriorated due to a difference in intensity at the surrounding portion of the LCD panel for the mobile communication system 50. In order to decrease a size of the mobile communication system while maintaining a sufficient liquid crystal display area, an area of the display portion of the LCD panel should be kept constant and an area of the surrounding portion of the LCD panel should be reduced. Accordingly, an area of the black matrix is also reduced, thereby subjecting the mobile communication system to a light leakage phenomenon.